Its says inHarry Potter and the Deathly Hallowswhen Luna and Dean were talking at Shell Cottage, Luna describes them to have "Small ears, a bit like a hippos, and covered with purple hair". I'm not wich chapter for sure, but its in there. *Luna(Talk) 22:30, December 15, 2010 (UTC)
Found it, “. . . and tiny little ears,” Luna was saying, “a bit like hippo’s, Daddy says, only purple and hairy. And if you want to call them, you have to hum; they prefer a waltz, nothing too fast. . . .” It's in chapter 25. --BachLynn(Accio!) 22:50, December 15, 2010 (UTC)
It should be added that the CHS can't fly. That's mentioned by Luna in the Order of the Phoenix, shortly after Ron calls that creature a Kacky Snorgle.